Passage of Uranium Fission Fragments Through Matter

Abstract

The ranges and rates of energy loss of the fission fragments of uranium are calculated on the basis of a model in which the charge of the fragment is obtained from its energy and its successive ionization potentials. The energy loss cross section for protons of the same velocity is then used to calculate the ranges of the two groups of fragments. For (${Z}_{1}=42$, ${A}_{1}=100$) and (${Z}_{2}=50$, ${A}_{2}=136$) these are found to be 2.42 cm and 2.08 cm, respectively, for a total assumed kinetic energy of 188 Mev and a final kinetic energy of the lighter fragment of 5 Mev (corresponding to ionization-chamber background). These are in fair agreement with the observed ranges of 2.2 cm and 1.5 cm. The experimental and theoretical range-energy relations are also in fair agreement. The validity of the model is discussed in detail, and it appears that it should be fairly good for fragments above 5 Mev. The initial charges of the fission fragments are found to be 17 and 13, respectively, and these are given as a function of the fragment energy in Table I. The density of ionization is found to decrease along the track, in marked contrast to the behavior for protons and alpha-particles.